The present invention relates generally to control knobs and more specifically to snap-on type attachment mechanisms for securing a control knob to a shaft.
Control knobs are ubiquitous in our society. They are used in a wide range of products ranging from consumer products for the home to laboratory instruments and, in particular, aircraft control panels.
Control knobs typically attached to a control shaft thereby allowing an operator to easily manipulate(e.g. rotate) the control shaft. Knobs are attached to the shafts in numerous ways including screws, glue, clips, welds, bolts, cotter pins, and numerous other types of fasteners.
One particular application of control knobs are in the aviation industry Due to the demanding environment of an aircraft cockpit, avionics control knobs must meet or exceed strict regulation standards and pilot expectations One important aspect of theses regulations and expectations is illumination of control knobs Proper illumination is critical in an aircraft control panel for assisting a pilot to quickly locate and assess the status of a knob or associated control panel Precise illumination is even more critical at night when a pilot must locate and assess control knobs in reduced ambient light conditions.
To satisfy these illumination requirements the prior art uses carefully constructed control panels and control knobs The knobs are at least partially constructed of a translucent plastic material so that light from a light source is conducted through the knob to cause the desired illumination. For example, such a knob may be designed to illuminate a ring around the base of a knob or to illuminate a symbol(e.g. a pointer or letter) on the end of the knob.
To achieve this controlled illumination the knobs are painted to eliminate all light leaks except where light illumination is desired. Once the knobs are painted they must be carefully handled since a scratch in the paint often causes an unacceptable light leak requiring the scratched area to be repainted.
A second aspect of the regulations and expectations is positive connection of the knob to the shaft. It is undesirable to have any looseness or free play between the knob and shaft. To achieve the required positive connection the prior art uses two set screws to secure the knob to the shaft.
The problem of light leaks is exacerbated by the use of the set screws because scratches are easily caused by the tool used to tighten the set screws. When a scratch occurs the knob must be returned to the paint shop for touch up. Often the entire circuit card to which the knob and shaft are attached must be sent to the paint shop. The repair, therefore, not only results in wasted time and cost associated with touching up the knob, but also exposes the circuit card to the risk of damage. Second, if a knob is scratched for any reason after the control panel has been assembled then the control panel must be disassembled in order to remove the knob. In either case there is wasted time and excessive cost.
Manufacture and repair of aircraft control panels and the like would be improved by a control knob which is not scratched by installation tools, may be removed without disassembling the control panel, and provides a positive attachment between the knob and control
Clearly there exists the need for a control knob attachment assembly which provides the benefits described above.